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  • Resultat 1-10 av 477
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1.
  • Belonoshko, Anatoly B., et al. (författare)
  • Quasi ab initio molecular dynamic study of Cu melting
  • 2000
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 61:6, s. 3838-3844
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the melting of Cu theoretically by means of a molecular dynamic method employing the Sutton-Chen model for the interatomic interaction. This interaction has been fitted to reproduce results from first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential linear-muffin-tin-orbital method for the bcc, fee, hcp, and liquid configurations. No experimental data were used to tune the potential. A large number of properties including equation of state, melting temperature, high-pressure melting curve, change of volume and entropy at melting, liquid structure, diffusion coefficient in liquid, and vacancy formation energy are all in good agreement with experimental data. Inclusion of the full potential energy of a liquid configuration in the fitting procedure is critical for obtaining good agreement with experiment. Different ways to calculate the melting transition are shown to produce very different results. The use of a large number of particles in combination with the solid-liquid interface as an initial configuration in the simulation is essential in order to obtain the correct melting temperatures.
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2.
  • Isaeva, E. I., et al. (författare)
  • Ab initio phonon calculations for Ll(2) Ni3Al and B2NiAl
  • 2004
  • Ingår i: Solid State Communications. - 0038-1098. ; 129:12, s. 809-814
  • Tidskriftsartikel (refereegranskat)abstract
    • The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available experimental results from inelastic neutron scattering.
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3.
  • Grigoriev, A., et al. (författare)
  • Electron transport in stretched monoatomic gold wires
  • 2006
  • Ingår i: Physical Review Letters. - 0031-9007. ; 97:23, s. 236807
  • Tidskriftsartikel (refereegranskat)abstract
    • The conductance of monoatomic gold wires containing 3-7 gold atoms has been obtained from ab initio calculations. The transmission is found to vary significantly depending on the wire stretching and the number of incorporated atoms. Such oscillations are determined by the electronic structure of the one-dimensional (1D) part of the wire between the contacts. Our results indicate that the conductivity of 1D wires can be suppressed without breaking the contact.
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4.
  • Abrikosov, I. A., et al. (författare)
  • Valence-band hybridization and core level shifts in random Ag-Pd alloys
  • 2001
  • Ingår i: Physical Review Letters. - 0031-9007. ; 8717:17
  • Tidskriftsartikel (refereegranskat)abstract
    • First-principles calculations of the core-level binding energy shifts (CLS) for 3d inner-core electrons of Ag and Pd in fcc Ag-Pd alloy were carried out within the complete screening picture, which includes both initial and final state effects. These allo
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5.
  • Ahuja, R., et al. (författare)
  • Electronic and optical properties of lead iodide
  • 2002
  • Ingår i: Journal of Applied Physics. - 0021-8979. ; 92:12, s. 7219-7224
  • Tidskriftsartikel (refereegranskat)abstract
    • Electronic and optical properties of lead iodide were studied experimentally using absorption, transmission, ellipsometry, and theoretically using a full-potential linear muffin-tin-orbital method. The samples were mounted in a closed-cycle helium refrigeration system and studied at temperatures between 10 and 300 K. Band-gap energy of lead iodide was measured as a function of temperature using optical absorption. Calculations showed that there was a small anisotropy in optical properties of lead iodide, and dielectric function calculations agreed well with experiments.
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6.
  • Ahuja, Rajeev, et al. (författare)
  • Optical properties of 4H-SiC
  • 2002
  • Ingår i: Journal of Applied Physics. - 0021-8979. ; 91:3, s. 2099-2103
  • Tidskriftsartikel (refereegranskat)abstract
    • The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies. © 2002 American Institute of Physics.
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7.
  • Andersson, David A., et al. (författare)
  • Redox properties of CeO2-MO2 MO2 (M=Ti, Zr, Hf or Th) solid solutions from first principles calculations
  • 2007
  • Ingår i: Applied Physics Letters. - 0003-6951. ; 90:3, s. 031909
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors have used density functional theory calculations to investigate how the redox thermodynamics and kinetics of CeO2 are influenced by forming solid solutions with TiO2, ZrO2, HfO2, and ThO2. Reduction is facilitated by dissolving TiO2 (largest improvement), HfO2, or ZrO2 (least improvement), while ThO2 makes reduction slightly more difficult. The migration barrier is much lower in the neighborhood of a Ti (largest decrease), Hf, or Zr (least decrease), while the binding energy of solute ions and vacancies increases in the same sequence. They rationalize the properties of ceria solid solutions in terms of defect cluster relaxations.
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8.
  • Andersson, David A., et al. (författare)
  • Theoretical study of CeO(2) doped with tetravalent ions
  • 2007
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829. ; 76:7, s. 174119
  • Tidskriftsartikel (refereegranskat)abstract
    • We have used density functional theory calculations within the LDA+U formulation to investigate how small amounts of dissolved SiO2, GeO2, SnO2, or PbO2 affect the redox thermodynamics of ceria (CeO2). Compared to pure ceria, reduction is facilitated and the reducibility increases in the sequence of CeO2-SnO2, CeO2-GeO2, and CeO2-SiO2, which correlates with the decrease of the ionic radii of the solutes. For low solute concentrations, there is an inverse relation between high reducibility and the solution energy of tetravalent solutes. CeO2-PbO2 is unique in the sense that the initial reduction occurs by Pb(IV)double right arrow Pb(II) instead of the usual Ce(IV)double right arrow Ce(III) reaction. Among the investigated ceria compounds, CeO2-PbO2 has the lowest reduction energy and rather low solution energy. We have studied how the solution and reduction energies depend on the concentration of Si, Ge, Sn, Pb, Ti, Zr, Hf, and Th solute ions. While the solution energy increases monotonously with concentration, the reduction energy first decreases, as compared to pure ceria (except for Th, which exhibits a small increase), and with further increase of solute concentration, it either remains almost constant (Zr, Hf, and Th) or slightly increases (Ti, Si, Ge, and Sn).
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9.
  • Belonoshko, Anatoly B., et al. (författare)
  • Molybdenum at High Pressure and Temperature : Melting from Another Solid Phase
  • 2008
  • Ingår i: Physical review letters / publ. by the American Physical Society. ; 100:13, s. 135701-1-135701-4
  • Tidskriftsartikel (refereegranskat)abstract
    •  The Gibbs free energies of bcc and fcc Mo are calculated from first principles in the quasiharmonic approximation in the pressure range from 350 to 850 GPa at room temperatures up to 7500 K. It is found that Mo, stable in the bcc phase at low temperatures, has lower free energy in the fcc structure than in the bcc phase at elevated temperatures. Our density-functional-theory-based molecular dynamics simulations demonstrate that fcc melts at higher than bcc temperatures above 1.5 Mbar. Our calculated melting temperatures and bcc-fcc boundary are consistent with the Mo Hugoniot sound speed measurements. We find that melting occurs at temperatures significantly above the bcc-fcc boundary. This suggests an explanation of the recent diamond anvil cell experiments, which find a phase boundary in the vicinity of our extrapolated bcc-fcc boundary.
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10.
  • Belonoshko, Anatoly B., et al. (författare)
  • Quenching of bcc-Fe from high to room temperature at high-pressure conditions : a molecular dynamics simulation
  • 2009
  • Ingår i: NEW JOURNAL OF PHYSICS. - 1367-2630. ; 11, s. 093039
  • Tidskriftsartikel (refereegranskat)abstract
    • The new high-temperature (T), high-pressure (P), body-centered cubic (bcc) phase of iron has probably already been synthesized in recent diamond anvil cell (DAC) experiments (Mikhaylushkin et al 2007 Phys. Rev. Lett. 99 165505). These DAC experiments on iron revealed that the high-PT phase on quenching transforms into a mixture of close-packed phases. Our molecular dynamics simulation and structural analysis allow us to provide a probable interpretation of the experiments. We show that quenching of the high-PT bcc phase simulated with the embedded-atom model also leads to the formation of the mixture of close-packed phases. Therefore, the assumption of the stability of the high-PT bcc iron phase is consistent with experimental observation.
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